1. Field of the Invention
The present invention relates to a variable speed motor, and more particularly to a variable speed motor for use in a motor capable of receiving single-phase Alternating Current (AC) power, which includes windings mounted to a stator of the motor to form poles, and a relay for connecting the windings in series or in parallel to each other to control speed of the motor, such that it can properly vary a rotation speed of the motor.
2. Description of the Related Art
FIG. 1 is an exploded perspective view of a rotor and a stator contained in a conventional outer-rotation motor. FIG. 2 is a motor winding arrangement illustrating a layout of a conventional 6-pole winding.
Typically, a motor includes a stator to which windings are mounted, a permanent magnet, and a rotator formed of an Al (aluminum) conductor or iron core. The motor generates periodic current variation in the winding mounted to the stator, torque occurs in the rotor by a constant variation of a magnetic field depending on current variation, such that the motor can acquire rotation power by the torque.
The motor is classified into an inner-rotation motor and an outer-rotation motor according to positions of the stator and the rotor. Particularly, the outer-rotation motor installs the stator into the rotor, such that the rotor is rotated by variation in current flowing in the winding of the stator, as shown in FIG. 1.
If the stator winding composed of two winding parts forms six poles as shown in FIG. 2, each of the winding parts forms three poles in the stator, and allows a direction of the winding to be inverted. Therefore, if a single-phase AC power signal is applied to the stator, a current direction capable of forming an adjacent pole is inverted, and a polarity of a magnetic field generated by the inverted current direction is classified into an N-pole and an S-pole, such that the N-pole and the S-pole are alternately generated.
In the meantime, if a single-phase AC voltage signal is applied to a conventional single-phase induction motor, a back electromotive force is generated in a primary winding mounted to the stator, and a back electromotive force is generated in a secondary winding mounted to a conductor of the rotor by the magnetic field generated from the stator winding, such that torque is generated to rotate the rotor.
However, if the single-phase AC power signal is applied to the single-phase induction motor, the single-phase induction motor does not generate rotation force, and generates an alternating magnetic field whose magnitude is changed in the direction of a winding axis, such that it additionally requires a starting device for initially starting the motor. In this case, the single-phase induction motor is classified into a split-phase start motor, shaded-coil type motor, a capacitor-operation motor, and a repulsion start motor according to categories of the starting device.
For example, the capacitor motor widely used will hereinafter be described with reference to FIG. 3.
FIG. 3 is an equivalent circuit of a conventional capacitor-type single-phase induction motor. Referring to FIG. 3, the capacitor-type single-phase induction motor includes a main winding L1, an auxiliary winding L2, and a capacitor C connected to the auxiliary winding L2 in series. If a single-phase AC power signal E1 is applied to the capacitor-type single-phase induction motor, an alternating magnetic field is generated in the main winding L1. In this case, the capacitor C controls a phase of a current signal flowing in the auxiliary winding L2 to be preceded by a predetermined angle of 90°, such that an auxiliary magnetic field having a phase difference of 90° compared with the alternating magnetic field of the main winding L1 is generated in the auxiliary winding L2.
Therefore, the alternating magnetic field generated from the main winding L1 and the auxiliary magnetic field generated from the auxiliary winding L2 have different magnetic field phases, such that they are not compensated, but are summed. As a result, a rotation magnetic field is generated, such that the single-phase induction motor is rotated.
If the conventional capacitor-type single-phase induction motor is applied to a washing machine, there is a need for the single-phase induction motor to be rotated at high or low speed according to a washing process. The above-mentioned single-phase induction motor can maintain a constant rotation speed at a specific location at which torque of the motor meets a load torque curve, so that it requires an additional device capable of implementing a motor having a speed conversion function, and motor speed of the washing machine can be properly controlled.
Therefore, an inverter circuit or an additional drive circuit is added to a three-phase motor to control a rotation speed of the motor. In this case, the cost of production is greatly increased, so that the cost of production of a variable speed motor is also greatly increased. Therefore, many developers have conducted intensive research into a pole-change single-phase induction motor acting as a low-priced motor speed controller. A 2-pole/4-pole conversion single-phase induction motor generally used as a pole-change single-phase induction motor will hereinafter be described with reference to FIG. 4
FIG. 4 is a configuration of a conventional pole-change single-phase induction motor. As shown in FIG. 4, the conventional pole-change single-phase induction motor includes a 2-pole main winding (1a and 1b), a 2-pole auxiliary winding (2a and 2b), a 4-pole main winding (3a, 3b, 3c, and 3d), and a 4-pole auxiliary winding (4a, 4b, 4c, and 4d). In the case of 2-pole operation, the motor is driven by the 2-pole main winding and the 2-pole auxiliary winding. In the case of 4-pole operation, the motor is driven by the 4-pole main winding and the 4-pole auxiliary winding.
In other words, the above-mentioned pole-change single-phase induction motor includes a high-speed winding and a low-speed winding which are arranged independent of each other, such that the motor can be driven by 2-pole operations using 2-pole-associated windings in the case of a high-speed rotation, and the motor can be driven by 4-pole operations using 4-pole-associated windings in the case of a low-speed rotation. In this way, the above-mentioned pole-change single-phase induction motor can properly vary a rotation speed using individual windings.
However, the above-mentioned pole-change single-phase induction motor uses four windings to perform a pole-change operation, a cross-sectional area of a slot is increased, efficiency of the motor is greatly reduced by the increased core loss of the stator, and a minimum variable speed which can be implemented is also limited, such that it has difficulty in extending the range of a variable speed.